Patent GB-793747-A (GB)
Title: A method and means for automatically adjusting a measuring or observation instrument
IPC: G05D25/02
Filed: 1956-04-30
Abstract: 793,747. Photo-electric control of optical instruments. ZEISS-STIFTUNG, C., [trading as ZEISS, C.[firm of]]. April 30, 1956 [May 7 1955], No. 13129/56. Class 40 (3). An optical instrument is automatically adjusted to the point of maximum local variation of the illumination intensity of a radiation field; first coarsely by means of a voltage proportional to the first differential coefficient of the light flux emanating from the radiation field and then finely by means of a voltage proportional to the second differential coefficient of the light flux. The coarse adjustment may be carried out by an electric motor energized by constant voltage and connected and disconnected when a voltage proportional to the first derivative falls below or exceeds a minimum or maximum value respectively, and fine adjustment follows by another electric motor energized by a voltage proportional to the second derivative. The embodiments described pertain to a refractometer with a radiation field as illustrated by Fig. 1 a and b, showing the variation of light flux # as a function of the angle of rotation of the instrument α. Producing and utilizing a voltage proportaonal to d#/dα.-The light passed through slit 1 is equally divided, alternately interrupted by rotary shutter 3 and projected on to the photocathode of cell 6 whose amplified output A.C. component feeds a relay for connecting and disconnecting the coarse adjustment motor according to whether the voltage is less than or exceeds a predetermined value. The motor rotates the measuring prism of the refractometer via a control cam and a lever in an arrangement similar to that in Fig. 3, see below. Producing and utilizing a voltage proportional to d<SP>2</SP>#/dα<SP>2</SP>.-Measuring prism 9 (see Fig. 3) is rotatable about its axis 10 by lever 8 gliding on control cam 7 driven through gearing from motor 25. Light passes through slit 11, lens 12 whose focal point lies on partially reflecting separating face 16 of a prism 15, and lens 13 and prism 15 such that the central part of the light flux passing through slit 14 is reflected downwards; effectively three slits 17, 18, 19 are produced with the latter twice as wide as either of the other two. Rotating disc 20 interrupts the light passing through slits 17 and 18 simultaneously and separately from that through slit 19. After reflection the light reaches the photocathode of cell 22 whose output voltage is amplified, rectified in synchronism with the shutter rotation, and fed to motor 25 sensitive to phase and amplitude, its direction of rotation depending upon which one of the separated light fluxes striking the photo-cell has:the greater value. General.-The coarse adjustment motor rotates again by means not described as soon as its control voltage decreases below a predetermined adjustable minimum value, to cater for movement of local variation of illumination of the radiation field, e.g. during a change of the measured object. If the direction of rotation is incorrect the " coarse " motor is reversed manually, or automatically by a limit switch when it reaches an end position without the first derivative exceeding a predetermined minimum value; or the motor rotates in the same direction after reaching an end position and the control mechanism scanning the radiation field is automatically re-set to the start position. To produce first and second derivative voltages simultaneously, a partial reflecting mirror is placed between measuring prism 9 and the devices shown in Figs. 2 and 3, allowing one part of the light from the measuring prism to fall on slit 1 and the other part on slit 14. - As an alternative to the displacement of the radiation field as described above, diaphragms not described may be moved in the focal plane of the image-forming lens.